1. Field of the Invention
The present invention relates to a magnetic head used in a magnetic disk drive and, more particularly, to a magnetic head and a magnetic disk drive for perpendicular magnetic recording, which have structures and characteristics optimum for a higher track density and a smaller track pitch.
2. Description of the Related Art
Conventionally, in the field of computers, magnetic disk drives are widely used as large-capacity external storages which allow random access. As these magnetic disk drives are very popular, demands increasingly arise for magnetic disk drives having a larger memory capacity and a higher recording density.
In a magnetic disk drive, usually, a plurality of magnetic disks each obtained by forming a magnetic layer on a non-magnetic substrate are stacked and mounted on one rotating shaft. Magnetic heads for performing recording and reproduction on and from these magnetic disks are mounted to arms. These arms are driven by actuators, thereby positioning the magnetic heads.
In the magnetic disk drive having this structure, each magnetic head is arranged so as to access a desired portion on the disk surface which is rotated at a high speed during recording and reproduction of information, such that it will not be brought into direct contact with the disk surface but slightly flies above the disk surface. A signal is recorded on or reproduced from concentric tracks of the disk surface by the magnetic head.
In the magnetic disk drive, in order to satisfy the demand for the larger memory capacity, attempts have been made to increase the linear recording density of the disk, i.e., the recording density in the circumferential direction or to increase the track density, i.e., the recording density in the radial direction. Furthermore, in order to increase the recording density, studies of extremely low flying height recording or contact recording have extensively been made in recent years, with which recording/reproduction is performed by causing the magnetic head to fly extremely slightly above the magnetic disk or by bringing the magnetic head into almost contact with the magnetic disk.
As a method of increasing the linear recording density, perpendicular magnetic recording was proposed in 1975. According to the perpendicular magnetic recording, since demagnetization in a magnetization transition portion can be made very small as compared to conventional longitudinal magnetic recording having anisotropy in a longitudinal direction, the magnetization transition width can be decreased. Thus, high-density recording is enabled. It is known that in this perpendicular magnetic recording, when a magnetic head for perpendicular magnetic recording which uses strip-type soft magnetic thin films is used, a recording field in a more perpendicular direction can be obtained, which is effective for obtaining a higher density. A magnetic disk having a perpendicular double layered medium obtained by providing a soft magnetic underlayer under a magnetic recording layer having a perpendicular magnetic anisotropy, is also proposed to increase the recording and reproducing efficiency in the perpendicular magnetic recording scheme, thereby forming a sharper magnetization transition. When this magnetic disk is employed, demagnetization at the distal end of the magnetic head can be decreased due to the magnetic interaction of the magnetic head and the under layer, so that a larger magnetic field can be obtained in recording. In reproduction, similarly, demagnetization at the distal end of the magnetic head can be decreased, so that the effective magnetic permeability can be increased. As a result, the magnetic flux emanating from the medium can be efficiently converged on the magnetic head, thereby obtaining a more intense signal.
In order to obtain a magnetic flux from a magnetization transition portion of a medium on which perpendicular recording has been performed efficiently, it is important that the magnetic head is moved close to the surface of the medium. For this reason, a conventional magnetic head for perpendicular recording is used to be brought into contact with the surface of a medium. However, the conventional magnetic head has problems in durability and wear resistance.
With the perpendicular magnetic recording scheme, magnetization is set upward or downward in the perpendicular direction with respect to the surface of the medium. Even if a 1-bit length is small, magnetization which is stable in terms of energy can be left in the recording layer of the medium. Therefore, the perpendicular magnetic recording scheme has been regarded as a method which is effective for realizing a higher density in principle. With the state-of-the-art perpendicular magnetic recording medium, however, as the recording magnetic field and inclination of the magnetic field are insufficient, satisfactory recording cannot be made on the medium. For this reason, a magnetic head having a higher recording ability than the conventional magnetic head has been demanded.